N-Rays Vs. N Rays: Will The Real N-Ray Please Stand Up?

There’s a problem with calling neutron radiography “N-ray.” And that problem is… “N rays” already exist. Or, rather, “N rays” don’t exist.


In the NDT community, neutron imaging, a powerful form of radiography first demonstrated in the 1930s soon after the discovery of the neutron, is often referred to as “N-ray” as a way to compare and contrast it to its more well-known cousin, X-ray imaging. “N-ray” is an informal, but industry-standard term recognized widely by nondestructive testing professionals across the world.

However, there’s a problem with calling neutron radiography “N-ray.” And that problem is… “N rays” already exist.

Or, rather, “N rays” don’t exist.

Power up your flux capacitor, slingshot your warp-capable starship around the sun, or hop into your nearest magic phone booth or extradimensional police box and take a trip to the halcyon days of the dawn of the 20th century to hear a cautionary tale of scientific hubris and trend-chasing.

Prosper-Rene Blondlot
Prosper-René Blondlot thought he’d made the scientific find of a lifetime. Spoiler alert: He hadn’t.

The Sobering Saga of N Rays

The late 19th Century and early 20th century was a boom period for experimental physics. Across America and Europe, everywhere you turned seemed to have a new scientist discovering some new thing. Victor Schumann discovered ultraviolet radiation in 1893; Wilhelm Rontgen discovered X-rays in 1895; Henri Becquerel discovered the very next year that uranium salts emitted rays very similar to X-rays. Around the same time when J. J. Thompson discovered electrons, Marie Curie and her husband discovered both radium and polonium and coined the term radioactivity to describe the emission of the high-energy rays Becquerel had discovered. Radiography as a tool in medicine and industry took off almost immediately on the heels of these new discoveries.

The 1890s closed out and a new century began with the whole physics community caught in the grip of radiation fever. Everybody was on the edge of their seats wondering what new form of radiation would be discovered next.

Enter Prosper-René Blondlot. Blondlot was a professor of physics at the University of Nancy in France with a keen interest in the burgeoning field of electromagnetic radiation. A highly-respected, prizewinning figure in the scientific community, he was a corresponding member of the French Academy of Sciences, and his work measuring the speed of electromagnetic waves won him commendations from other titans of physics, including J. J. Thompson and Henri Poincaré.

In other words, Blondlot was an intelligent, accomplished man of science. As a result, when he claimed to have discovered a new form of radiation in 1903, his peers’ ears perked up.

The Discovery of N Rays

Blondlot’s new form of radiation, which he had discovered while attempting to polarize X-rays, was dubbed “N ray” in honor of the University of Nancy. N rays were discovered when Blondlot measured changes in the brightness of an electric spark in the gap between two conducting electrodes used in his X-ray experiments.

And by “measured the changes,” what we mean is that he saw the electric spark flicker a bit out of the corner of his eye. Hardly the most rigorous way to measure something, but who can blame the poor guy for being a little overexcited about making his mark on a field where new discoveries were being made every year?

These strange, elusive N rays, his further experiments claimed, could be detected only by refracting them through an aluminum prism on their way to collide with a thread of calcium sulfide. The thread would glow in the dark ever so slightly if looked at out of the corner of your eye, which was more or less his sole physical proof that N rays existed.

Blondlot's dubious proof of "N rays"
Blondlot’s “proof” of N rays.

After Blondlot’s initial discovery, over one hundred other scientists in France published articles claiming to be able to detect N rays as well. It seemed N rays were seemingly emitted by just about every substance known to man, including the human body, with two odd exceptions: Freshly-cut wood (also known as “green wood”) and certain kinds of treated metals. N rays, apparently, were just about everywhere, but had bizarre and nonsensical properties.

N rays passed straight through opaque materials like wood, aluminum, and paper, but were stopped by some materials visible light could pass through (like water). Funnily enough, real N-rays, neutron radiation, have similar properties (passing easily through many dense substances, yet struggling to penetrate lighter and hydrogen-rich substances such as water), which is what makes them such a great tool for industrial radiography.

Outside of France, though, physicists who were initially excited about the discovery of this strange new form of radiation were stymied as they sought to recreate Blondlot’s method for detecting N rays—even as scientists smitten with the elusive rays continued to announce the remarkable properties they had discovered in their recreations of Blondlot’s experiments.

The Debunking of N Rays

One of the many frustrated scientists was Robert Williams Wood, an American physicist and inventor. His love affair with physics had begun when he, as a young boy, had witnessed an aurora dancing across the sky. Enthralled by the sight, he had dedicated himself to discovering what invisible rays could produce such a gorgeous phenomenon.

Though he was best known for his work in optics, Wood also had a reputation as a debunker of pseudoscience. For this reason, the British journal Nature asked him to travel to Blondlot’s lab to investigate his experiments.

"I went, I must confess,” he began his subsequent article in Nature, “in a doubting frame of mind, but with the hope that I might be convinced of the reality of this phenomena, the accounts of which have been read with so much scepticism."

Robert Williams Wood
American physicist and inventor

Wood was unimpressed by what he saw when Blondlot and his assistant performed his experiment in front of him. For over three hours, he watched and waited with an open mind, hoping that his skepticism would be proven wrong, but nothing he was shown proved conclusive in the least bit.

As the test dragged on, Wood decided to engage in some surreptitious sabotage. In the darkened room, Wood quietly removed the aluminum prism from the testing apparatus. Lo and behold, Blondlot and his assistant continued to “see” N rays while Wood, predictably, saw nothing. Next, he swapped out a large steel file Blondlot claimed to be emitting N rays with a piece of inert wood. Blondlot still detected N rays.

Robert W. Wood, an early 20th Century mythbuster

It was clear that N rays were nothing more than a shared delusion. Blondlot, his assistant, and other scientists who’d repeated the experiment had, in their eagerness to advance scientific understanding, only seen what they’d wanted to see. Wood concluded his article for Nature, published September 1904, thusly:

“After spending three hours or more in witnessing various experiments, I am not only unable to report a single observation which appeared to indicate the existence of the rays, but left with a very firm conviction that the few experimenters who have obtained positive results, have been in some way deluded.”


The Lasting Legacy of N Rays

Wood’s report on his findings was published in Nature in 1904. By 1905, no one in the scientific community believed that N rays existed anymore—except for Blondlot, that is, who remained convinced of their existence to the very end, having outlived his own career by twenty years.

The most tragic part of this story is that Blondlot was an accomplished and respected scientist before announcing his discovery. Humans are pattern-seeking creatures; when our imaginations kick into overdrive, we can find ourselves seeing things that aren’t there, like faces on pieces of toast or meaningful signals within bursts of noise. Blondlot’s downfall was just a form of scientific pareidolia that grew big enough to sweep him off his feet.

Today, the story of Blondlot and his too-good-to-be-true N rays lives on as a testament to an important truth: That while scientists are just as fallible and susceptible to trend-chasing, the institution of science is still a self-correcting one, in which errors and falsehoods are eventually found out and snuffed out (and in the case of N rays, rather quickly). Whether it’s a flawed or incomplete theory or downright pseudoscience, sooner or later someone comes along with a better idea which dethrones the old one.

It’s also left a bit of a pickle for radiography specialists in the nondestructive testing community, who have seized on “N-ray” as a convenient, catchy shorthand for “neutron radiography.” Neutron radiation, unlike Blondlot’s N rays, is a very real phenomenon, and is incredibly useful for quality assurance, failure analysis, and other forms of materials testing. By harnessing neutron radiation in a similar way as X-rays, you can paint a picture of an object’s internal structure. And because neutron radiation interacts with materials very differently than X-rays, you can see details that X-ray imaging alone wouldn’t be able to show you.

Neutrons, the neutral particles found within atomic nuclei, were discovered by James Chadwick in 1932. By the end of the decade, researchers discovered that neutrons could easily pass through many dense materials that X-rays tended to struggle with, making them a potentially powerful tool for industrial radiography; however, it wasn’t until the 1950s that technology developed to the point that detailed, quality neutron images could be produced. By the time neutron imaging became an established testing method in NDT (albeit, due to the high neutron fluxes required, not a very often-used one), Blondlot’s N rays had been all but forgotten.

And then, over the past decade, they had a little bit of a resurgence in popularity. Not because people started thinking they existed (thank heavens), but rather because tech and pop sci writers realized it was really fun to write articles about Blondlot’s short-lived, well-intentioned hoax.

In all honesty, they were right. It is.

Because the story behind them is so fascinating (and funny, albeit at poor Blondlot’s expense), the fictitious N rays, once left to fade away into obscurity, have ended up getting a lot more attention than real N-rays (just ask your favorite search engine). This can make it a little frustrating for professionals in the neutron imaging community (like us) who might feel a little embarrassed when the people they’ve talked to at their most recent NDT trade show or business convention go home and google “N-ray” only to find a notorious example of a short-lived scientific hoax all over the first page of search results.

Granted, there are worse things to be upset over, such as sharing a name with Michael Bolton. We neutron imaging professionals take solace in the fact that while we may have not been here first, at least we actually exist.

Learn more about real N-rays